Acetic acid bacteria are microorganisms broadly utilized for vinegar production. In particular, acetic acid bacteria belonging to the genus Acetobacter or the same belonging to the genus Gluconacetobacter are utilized for industrial acetic acid fermentation.
In acetic acid fermentation, ethanol in media is oxidized and converted into acetic acid by acetic acid bacteria, and as a result, acetic acid is accumulated in the media. However, acetic acid has an inhibitory action on acetic acid bacteria. As the amount of accumulated acetic acid increases and the acetic acid concentration in media becomes higher, the growth ability and the fermentation ability of acetic acid bacteria gradually decrease.
In particular, growth induction period, that is, the period until acetic acid bacteria actually start to grow, and then it becomes possible to confirm the accumulation of acetic acid, tends to be longer as acetic acid concentration becomes higher.
Hence, in acetic acid fermentation, it is desired to further shorten the growth induction period, even in the case of a high acetic acid concentration. As a means for this purpose, a method has been reported that involves adding PQQ (4,5-dihydro-4,5-dioxo-1H-pyrrolo [2,3-f] quinoline-2,7,9-tricarboxylic acid) to a fermentation liquid to promote growth, so as to shorten so-called the growth induction period (e.g., see Patent document 1).
However, obtainment of PQQ in large quantities is difficult and PQQ is expensive. Thus, implementation of such a method at industrial scale is always associated with problems. Accordingly, it has been attempted to breed and improve acetic acid bacteria by promoting the growth of acetic acid bacteria, cloning genes (growth-promoting genes) encoding proteins having a function capable of shortening so-called the growth induction period, and using the growth-promoting genes.
However, no genes involved in growth promotion of acetic acid bacteria have been isolated so far. Under such circumstances, isolation of a novel growth-promoting gene encoding a protein having a function of promoting the growth of acetic acid bacteria at practical level and of shortening the growth induction period and breeding of acetic acid bacteria having a stronger growth function using the growth-promoting gene have been desired.    Patent document 1: JP Patent Publication (Kokai) No. 61-58584 A (1986)    Patent document 2: JP Patent Publication (Kokai) No. 60-9488 A (1985)    Patent document 3: JP Patent Publication (Kokai) No. 60-9489 A (1985)    Patent document 4: Specification of JP Patent Application No. 2003-350265    Non-patent document 1: “Biochimica et Biophysica Acta,” vol. 1088, pp. 292-300, 1991    Non-patent document 2: “Applied and Environmental Microbiology,” vol. 55, pp. 171-176, 1989    Non-patent document 3: “Agricultural and Biological Chemistry,” vol. 52, pp. 3125-3129, 1988    Non-patent document 4: “Agricultural and Biological Chemistry,” vol. 49, pp. 2091-2097, 1985    Non-patent document 5: “Bioscience, Biotechnology and Biochemistry,” vol. 58, pp. 974-975, 1994    Non-patent document 6: “European Journal of Biochemistry,” vol. 254, pp. 356-362, 1998    Non-patent document 7: “Methods in Enzymology,” vol. 89, pp. 450-457, 1982    Non-patent document 8: “Methods in Enzymology,” vol. 89, pp. 491-496, 1982    Non-patent document 9: “Cellulose,” pp. 153-158, 1989